Spikes detected in Type II metric Radio bursts

Spyridon Armatas, National and Kapodistrian University of Athens

We report the detection of Type II-associated spike-like structures, in dynamic spectra obtained with the Artemis-JLS (ARTEMIS-IV) solar radio spectrograph. We selected 4 events recorded by the Artemis-JLS/SAO receiver in the 270-450 MHz range; the high time resolution (10ms) of this receiver facilitates fine structure detection and analysis on dynamic spectra. The spike-like structures observed were found to co-exist with herring-bones or pulsations. More than 600 short narrowband spikes were identified and their parameters (duration, bandwidth) were computed. These structures mainly appear in chains which drift almost parallel to the harmonic emission band of the Type II front, which is within the frequency range of the SAO receiver. Single isolated bursts have been rarely detected. The average duration and relative bandwidth were about 96 ms and 1.7% respectively. These values are very close to those of the spikes embedded in Type IV bursts, in the same frequency range. Small-scale reconnection along the front of the Type II burst could be the origin of the detected spikes.